Crossing over refers to an event taking place in the cells undergoing meiosis cell division during which the exchange of material takes place. The process of crossing over takes place during pachytene of prophase I in meiosis I.
Crossing over takes place when the structure formed by the pairing of the four chromatids of the chromosomes called tetrad is formed. The formation of tetrad allows the exchange of genetic sequences, therefore, result in recombination.
The process of crossing over does not take place in the mitosis as the tetrad is not formed in the mitosis.
